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Knee Extensor Injuries

(Quadriceps Tendon Tear; Patellar Tendon Tear; Patellar Fracture; Tibial Tubercle Fracture)

By Danielle Campagne, MD, Assistant Clinical Professor, Department of Emergency Medicine, University of San Francisco - Fresno

Knee extensor injuries occur when people try to straighten (extend) their knee and an obstacle prevents them from doing so. Such injuries can tear the tendon that attaches the main muscle in the thigh (quadriceps) to the kneecap (patella), tear the tendon that attaches the kneecap to the shinbone (tibia), or break the kneecap or top of the shinbone.

In healthy people, knee extensor injuries occur only when force is significant (as occurs in a jump from a height or in high-impact car crashes). However, people may have certain conditions that make these injuries more likely. These conditions include

People with one of these conditions can injure their knee when they stumble on stairs or catch their foot when walking.

The quadriceps tendon attaches the main muscle in the thigh (quadriceps) to the kneecap (patella). The patellar tendon attaches the kneecap to the shinbone (tibia).

Extending the Knee

Extending the knee involves several structures, which can be injured when people try to straighten their knee and are blocked from doing so. These injuries include

  • A tear (rupture) in the quadriceps tendon, which attaches the main muscle in the thigh (quadriceps) to the kneecap (patella)

  • A tear in the patellar tendon, which attaches the kneecap to the shinbone (tibia)

  • Fracture of the kneecap or top of the shinbone

Symptoms

If a tendon is completely torn, people cannot stand or extend their knee while seated. The knee is usually painful and swollen.

The kneecap may be out of place (displaced), above or below its usual location.

Diagnosis

  • A doctor's evaluation

  • X-rays

  • Magnetic resonance imaging

By examining the knee, doctors may be able to tell which structure is injured. If a person has knee swelling and pain after an injury, doctors ask the person to try to extend the injured leg. If the person cannot extend the leg, a knee extensor mechanism injury is likely.

Doctors also take x-rays of the knee. Often, x-rays can show whether a kneecap is displaced or fractured, but x-rays but may appear normal or show a knee cap that is positioned higher than its usual place over the knee joint (called a high-riding or raised patella).

Magnetic resonance imaging (MRI) is needed to confirm the diagnosis.

Treatment

  • Surgery

Knee extensor injuries are surgically repaired as soon as possible.

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